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  Subjects -> ENGINEERING (Total: 1957 journals)
    - CHEMICAL ENGINEERING (150 journals)
    - CIVIL ENGINEERING (146 journals)
    - ELECTRICAL ENGINEERING (84 journals)
    - ENGINEERING (1124 journals)
    - ENGINEERING MECHANICS AND MATERIALS (284 journals)
    - HYDRAULIC ENGINEERING (43 journals)
    - INDUSTRIAL ENGINEERING (53 journals)
    - MECHANICAL ENGINEERING (73 journals)

CHEMICAL ENGINEERING (150 journals)                  1 2     

ACS Combinatorial Science     Full-text available via subscription   (7 followers)
Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials     Hybrid Journal   (3 followers)
Acta Polymerica     Hybrid Journal   (4 followers)
Additives for Polymers     Full-text available via subscription   (17 followers)
Adhesion Adhesives & Sealants     Hybrid Journal   (3 followers)
Advanced Chemical Engineering Research     Open Access   (7 followers)
Advances in Applied Ceramics     Partially Free   (2 followers)
Advances in Chemical Engineering     Full-text available via subscription   (14 followers)
Advances in Chemical Engineering and Science     Open Access   (19 followers)
Advances in Polymer Technology     Hybrid Journal   (9 followers)
African Journal of Pure and Applied Chemistry     Open Access  
Annual Review of Analytical Chemistry     Full-text available via subscription   (8 followers)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (8 followers)
Anti-Corrosion Methods and Materials     Hybrid Journal   (3 followers)
Applied Petrochemical Research     Open Access   (3 followers)
Asia-Pacific Journal of Chemical Engineering     Hybrid Journal   (6 followers)
Biochemical Engineering Journal     Hybrid Journal   (8 followers)
Biomass Conversion and Biorefinery     Partially Free   (5 followers)
BMC Chemical Biology     Open Access   (4 followers)
Brazilian Journal of Chemical Engineering     Open Access   (2 followers)
Bulletin of the Chemical Society of Ethiopia     Open Access   (1 follower)
Carbohydrate Polymers     Hybrid Journal   (8 followers)
Catalysts     Open Access   (5 followers)
Chemical and Petroleum Engineering     Hybrid Journal   (7 followers)
Chemical and Process Engineering     Open Access   (3 followers)
Chemical and Process Engineering Research     Open Access   (5 followers)
Chemical Communications     Full-text available via subscription   (28 followers)
Chemical Engineering & Technology     Hybrid Journal   (24 followers)
Chemical Engineering and Processing: Process Intensification     Hybrid Journal   (9 followers)
Chemical Engineering and Science     Open Access   (2 followers)
Chemical Engineering Communications     Hybrid Journal   (10 followers)
Chemical Engineering Journal     Hybrid Journal   (16 followers)
Chemical Engineering Research and Design     Hybrid Journal   (15 followers)
Chemical Engineering Science     Hybrid Journal   (9 followers)
Chemical Geology     Hybrid Journal   (9 followers)
Chemical Papers     Hybrid Journal   (3 followers)
Chemical Product and Process Modeling     Full-text available via subscription   (3 followers)
Chemical Reviews     Full-text available via subscription   (187 followers)
Chemical Society Reviews     Full-text available via subscription   (26 followers)
Chemical Technology     Open Access   (4 followers)
ChemInform     Hybrid Journal   (3 followers)
Chemistry & Industry     Hybrid Journal   (2 followers)
Chemistry Central Journal     Open Access   (5 followers)
Chemistry of Materials     Full-text available via subscription   (137 followers)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (6 followers)
ChemSusChem     Hybrid Journal   (6 followers)
Chinese Chemical Letters     Full-text available via subscription   (1 follower)
Chinese Journal of Chemical Engineering     Full-text available via subscription   (3 followers)
Chinese Journal of Chemical Physics     Hybrid Journal   (1 follower)
Coke and Chemistry     Hybrid Journal  
Coloration Technology     Hybrid Journal   (1 follower)
Computational Biology and Chemistry     Hybrid Journal   (8 followers)
Computer Aided Chemical Engineering     Full-text available via subscription   (2 followers)
Computers & Chemical Engineering     Hybrid Journal   (6 followers)
Corrosion Engineering, Science and Technology     Hybrid Journal   (18 followers)
Corrosion Reviews     Full-text available via subscription   (4 followers)
Crystal Research and Technology     Hybrid Journal   (2 followers)
Current Opinion in Chemical Engineering     Open Access   (2 followers)
Education for Chemical Engineers     Hybrid Journal   (3 followers)
European Polymer Journal     Hybrid Journal   (41 followers)
Fibers and Polymers     Full-text available via subscription   (3 followers)
Focusing on Modern Food Industry     Open Access   (3 followers)
Frontiers of Chemical Science and Engineering     Hybrid Journal   (1 follower)
Geochemistry International     Hybrid Journal  
High Performance Polymers     Hybrid Journal  
Indian Chemical Engineer     Hybrid Journal   (3 followers)
Indian Journal of Chemical Technology (IJCT)     Open Access   (12 followers)
Industrial & Engineering Chemistry     Full-text available via subscription   (9 followers)
Industrial & Engineering Chemistry Research     Full-text available via subscription   (16 followers)
Industrial Chemistry Library     Full-text available via subscription   (4 followers)
International Journal of Chemical and Petroleum Sciences     Open Access   (1 follower)
International Journal of Chemical Engineering     Open Access   (6 followers)
International Journal of Chemical Reactor Engineering     Full-text available via subscription   (3 followers)
International Journal of Chemical Technology     Open Access   (3 followers)
International Journal of Chemoinformatics and Chemical Engineering     Full-text available via subscription   (2 followers)
International Journal of Food Science     Open Access   (2 followers)
International Journal of Industrial Chemistry     Open Access  
International Journal of Polymeric Materials     Hybrid Journal   (3 followers)
International Journal of Science and Engineering     Open Access   (7 followers)
International Journal of Waste Resources     Open Access   (3 followers)
ISRN Chemical Engineering     Open Access   (3 followers)
ISRN Polymer Science     Open Access   (10 followers)
Journal of Applied Crystallography     Hybrid Journal   (4 followers)
Journal of Applied Electrochemistry     Hybrid Journal   (6 followers)
Journal of Applied Polymer Science     Hybrid Journal   (124 followers)
Journal of Biomaterials Science, Polymer Edition     Hybrid Journal   (7 followers)
Journal of Chemical & Engineering Data     Full-text available via subscription   (6 followers)
Journal of Chemical Ecology     Hybrid Journal   (1 follower)
Journal of Chemical Engineering     Open Access   (3 followers)
Journal of Chemical Engineering and Materials Science     Open Access  
Journal of Chemical Science and Technology     Open Access   (1 follower)
Journal of Chemical Sciences     Partially Free   (13 followers)
Journal of Chemical Technology & Biotechnology     Hybrid Journal   (2 followers)
Journal of Chemical Theory and Computation     Full-text available via subscription   (8 followers)
Journal of Coatings     Open Access   (2 followers)
Journal of Crystallization Process and Technology     Open Access   (4 followers)
Journal of Food Measurement and Characterization     Hybrid Journal  
Journal of Fuel Chemistry and Technology     Full-text available via subscription   (5 followers)
Journal of Geochemical Exploration     Hybrid Journal  
Journal of Industrial and Engineering Chemistry     Hybrid Journal   (1 follower)

        1 2     

Chemical Engineering Science    [11 followers]  Follow    
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 0009-2509
     Published by Elsevier Homepage  [2556 journals]   [SJR: 1.033]   [H-I: 103]
  • Modelling mass transfer properties in a biotrickling filter for the
           removal of isopropanol
    • Abstract: Publication date: 28 April 2014
      Source:Chemical Engineering Science, Volume 108
      Author(s): Pau San-Valero , Josep M. Penya-Roja , F. Javier Álvarez-Hornos , Carmen Gabaldón
      A study was carried out to model mass transfer properties in biotrickling filters, treating isopropanol as the target pollutant. This study was extended to the mass transfer of oxygen related to the fact that the treatment of hydrophilic compounds by biotrickling filtration is often limited by oxygen. A simple method for each compound was developed based on their physical properties. The influence of temperature on Henry’s law constant of isopropanol was determined. An increase of 1.8 per 10°C for the dimensionless Henry’s law constant was obtained. The determination of the overall mass transfer coefficients of isopropanol (K G a) was carried out, obtaining values between 500 and 1800h−1 for gas velocities of 100 and 300mh−1. No significant influences were observed for either the liquid velocity or packing material. Also, the determination of overall mass transfer coefficients of oxygen (K L a) were carried out, obtaining values between 20 and 200h−1 depending on the packing material for liquid velocities between 2 and 33m h−1. Structured packing materials exhibited greater mass transfer coefficients, while for random packing materials, the mass transfer coefficients clearly benefited from the high specific surface area. Mathematical correlations found in the literature were compared with the empirical data, showing that neither was capable of reproducing the mass transfer coefficients obtained empirically. Thus, empirical relationships between the mass transfer coefficients and the gas and liquid velocities are proposed to characterise the system.


      PubDate: 2014-01-23T22:18:21Z
       
  • Catalytic fast pyrolysis of lignocellulosic biomass in a process
           development unit with continual catalyst addition and removal
    • Abstract: Publication date: 28 April 2014
      Source:Chemical Engineering Science, Volume 108
      Author(s): Jungho Jae , Robert Coolman , T.J. Mountziaris , George W. Huber
      Catalytic fast pyrolysis (CFP) of wood was studied using a spray-dried ZSM-5 catalyst in a process development unit (PDU) consisting of a bubbling fluidized bed reactor with on-stream particle input and output. The PDU was capable of maintaining constant product yield of aromatics over an extended reaction period (6h) with continuous catalyst addition and removal. The yields and selectivity for aromatics and olefins were dependent on temperature, biomass weight hourly space velocity (WHSV), catalyst to biomass ratio, fluidization gas velocity, and catalyst bed weight. The overall aromatic yield increased up to 15.5 carbon% with decreasing gas velocities due to the increased vapor residence time and the improved mass transfer from smaller bubble sizes. A simulated recycle stream of CFP product gases consisting of CO, CO2 and olefins was used to test the viability of subsequent olefin aromatization in the presence of CO and CO2. Olefins were converted into additional aromatics while CO and CO2 remained inert during CFP. The spray-dried ZSM-5 catalyst was stable in a series of 30 reaction/regeneration cycles.
      Graphical abstract image

      PubDate: 2014-01-23T22:18:21Z
       
  • Extruded polymer films for optimal enzyme-catalyzed oxygen scavenging
    • Abstract: Publication date: 28 April 2014
      Source:Chemical Engineering Science, Volume 108
      Author(s): Kristin Johansson , Sami Kotkamo , Bjørn Tore Rotabakk , Caisa Johansson , Jurkka Kuusipalo , Leif J. Jönsson , Lars Järnström
      The use of enzymes as oxygen scavengers has a great potential in the food packaging industry. Enzymes can be incorporated into a coating layer that can be applied directly onto the packaging material. For the system to be fully functional, there is however a need for the packaging to have some barrier properties, to be sealable through heat, and to ensure low or no migration of the active coating to the food. Various combinations of polypropylene (PP), poly(lactic acid) (PLA) and low density polyethylene (LDPE) were extruded onto board coated with the oxygen-scavenging enzyme. Properties such as oxygen-transmission rate, water-vapor transmission rate, heat-sealability, migration and oxygen scavenging capacity were evaluated. All combinations of extruded material resulted in a packaging material able to scavenge the oxygen at both 84% and 100% relative humidity. The greatest decrease in oxygen concentration of the head space of air-tight chambers was achieved with the material extruded with PLA on at least one side. It was found that the extruded plastic is necessary in order to meet the EU directives on migration from food packaging materials of not more than a total of 10mg/dm2 material. All plastics were heat sealable against themselves but not against any of the other plastics and only LDPE adhered strongly to the enzyme-containing coating.


      PubDate: 2014-01-23T22:18:21Z
       
  • Ideal and mixture permeation selectivity of flexible prototypical zeolitic
           imidazolate framework – 8 Membranes
    • Abstract: Publication date: 28 April 2014
      Source:Chemical Engineering Science, Volume 108
      Author(s): C. Sitprasert , F.Y. Wang , V. Rudolph , Z.H. Zhu
      Permeance, ideal and mixture permeation selectivity have been evaluated based on molecular simulations of gas adsorptions by the grand canonical Monte Carlo simulation and diffusion by molecular dynamics simulation under a flexible framework. Additional transport phenomena are also obtained using transition state theory under rigid framework assumptions. A number of gas systems in the simulation involving H2, CO2, CH4, N2, O2 and Ar penetrating through a thin layer of ZIF-8 membrane are analyzed and compared with permeance, ideal and mixture permeation selectivity experiments. Three contributions have been achieved in this work. Firstly, it is demonstrated that the assumption of a rigid framework may be sufficient for simulating adsorption isotherms while diffusivity requires a flexible framework, especially when a diffusing molecule is bigger than the pore window of the MOFs, with an appropriate force-field and charges. Secondly, simulations of the ideal permeation selectivity are higher than those of mixture permeation selectivity. However, both calculations with flexible framework accuracy may be acceptable for the purpose of screening membrane materials when compared with experiments, especially the permeation selectivity of an equimolar mixture. Finally, even though simulated isotherms, diffusivity and mixture selectivity are consistent with available experiments and the same data have been used for estimating permeance of the membrane, the difference between the estimation and measurement of the permeation at low pressure is considerable. Therefore, it is confirmed that the effects of defections and multi-scale (macroscopic) diffusion cannot be ignored.


      PubDate: 2014-01-19T21:27:18Z
       
  • Numerical study of bubble break-up in bubbly flows using a deterministic
           Euler–Lagrange framework
    • Abstract: Publication date: 28 April 2014
      Source:Chemical Engineering Science, Volume 108
      Author(s): Y.M. Lau , W. Bai , N.G. Deen , J.A.M. Kuipers
      In this work we present a numerical model to predict the bubble size distribution in turbulent bubbly flows. The continuous phase is described by the volume-averaged Navier–Stokes equations, which are solved on an Eulerian grid, whereas the dispersed or bubble phase is treated in a Lagrangian manner, where each individual bubble is tracked throughout the computational domain. Collisions between bubbles are described by means of a hard-sphere model. Coalescence of bubbles is modeled via a stochastic inter-particle encounter model. A break-up model is implemented with a break-up constraint on the basis of a critical Weber value augmented with a model for the daughter size distribution. A numerical parameter study is performed of the bubble break-up model implemented in the deterministic Euler–Lagrange framework and its effect on the bubble size distribution (BSD) is reported. A square bubble column operated at a superficial gas velocity of 2cm/s is chosen as a simulation base case to evaluate the parameters. The parameters that are varied are the values of the critical Weber number ( We crit ), the daughter size distribution (β) and the superficial gas velocity ( v sup ). Changes in the values of We crit and v sup have a significant impact on the overall BSD, while a different shaped β did not show a significant difference.
      Graphical abstract image Highlights

      PubDate: 2014-01-19T21:27:18Z
       
  • Experimental study on carbamate formation in the AMP–CO2–H2O
           system at different temperatures
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Arlinda F. Ciftja , Ardi Hartono , Hallvard F. Svendsen
      Carbamate formation in the 30wt% of 2-amino-2-methyl-1-propanol (AMP) system at different CO2 loadings and temperatures was studied via nuclear magnetic resonance (NMR) spectroscopy. The results indicate that the main species in this system are AMP/AMPH+, AMPCO2 − and HCO3 −/CO3 2−. The carbamate was also observed at low loadings and the apparent carbamate stability constant was estimated based on the experimental concentrations of the species from NMR analysis. Carbamate formation was found to have weak temperature dependence in the range tested (25–45°C). To distinguish within the AMP/AMPH+ and HCO3 −/CO3 2− pairs, the amine protonation constant, the dissociation constant of carbonic acid from literature, and pH measurements for different ionic strengths were all employed. All the data were correlated with ionic strength and temperature. The accuracy of the carbamate stability constant determined from the concentration measurements will depend on pK a , ionic strength (I) used to calculate the speciation and on the uncertainty in the species concentration determinations from NMR, particularly for the carbamate species at low CO2 loadings and high temperature.


      PubDate: 2014-01-15T21:07:17Z
       
  • Developing saponite supported cobalt–molybdenum catalysts for
           upgrading squalene, a hydrocarbon from the microalgae Botryococcus braunii
           
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Leonito O. Garciano II , Nguyen H. Tran , G.S. Kamali Kannangara , Adriyan S. Milev , Michael A. Wilson , Herbert Volk
      The long chain hydrocarbons derived from the microalgae Botryococcus braunii are potential source of liquid biofuels for oil refineries. However, there is room for catalyst development on treating these new oil sources since they differ from mineral oils. In this work, the cobalt–molybdenum catalysts supported on the phyllosilicate saponite (Al2O3–SiO2) have been used for upgrading squalene (C30H50) a hydrocarbon related to B. braunii oil. The saponite supported catalysts were synthesised with varying aluminium to silicon (Al:Si) ratios of 1:2, 1:10, 1:20, 1:30 and 1:50 using a non-hydrothermal method. The cobalt and molybdenum (Co:Mo) ratio remained unchanged at 5:1 during the synthesis. Characterisation of the saponite supported catalysts was carried out using X-ray diffraction (XRD), nitrogen gas adsorption, X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy. It appears that the catalysts with the Al:Si ratios of 1:2 and 1:10 incorporate aluminium into tetrahedral and octahedral sites. When the Al:Si ratios are reduced from 1:20 to 1:50, the aluminium occupies octahedral sites only. Catalytic upgrading of squalene using these catalysts was carried out at the temperature of 400°C with Formier gas (5% H2:95% N2). Nuclear magnetic resonance (NMR) and gas chromatography–mass spectrometry (GC–MS) analysis showed the formation of pentacyclic triterpenes with a double bond. In addition, the 1:2 saponite supported catalyst has hydrogenation, hydrocracking and esterification abilities by virtue of its capacity to adsorbed exchangeable protons and carboxylate groups. Removal of the adsorbed exchangeable protons caused structural collapse during the reaction for some catalysts. Nevertheless the 1:20, 1:30 and 1:50 saponite supported catalysts remained stable. Our results provide an understanding of reactions of saponites with squalene and the potential of the saponite supported catalysts in biofuel upgrading.
      Graphical abstract image

      PubDate: 2014-01-15T21:07:17Z
       
  • Porosity variation below a fluid–porous interface
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Arzhang Khalili , Mohammad Reza Morad , Maciej Matyka , Bo Liu , Reza Malekmohammadi , Jörg Weise , Marcel M.M. Kuypers
      The correct quantification of porosity is essential in all studies pertaining to porous media. A host of existing works employs a constant, bulk value for porosity, even when the porous sample is attached to a free fluid. Since the volume fraction of the solid matrix near the interface region differs from that in the core, the porosity undergoes a spatial variation. Here we present a novel relation for the porosity as a function of depth below the interface, using the concept of surface roughness applied on the classical definition of open porosity. This relation has been verified by computational modeling as well as non-invasive laser experiments. It has been shown that this depth-dependent porosity relation applies also to a non-granular porous layer such as a biofilm.


      PubDate: 2014-01-15T21:07:17Z
       
  • Concentration-independent rate constant for biodiesel synthesis from
           homogeneous-catalytic esterification of free fatty acid
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Saeikh Z. Hassan , Madhu Vinjamur
      Dependence of the second-order rate constant (SRC) on the reactants’ concentration, for esterification of fatty acids, is found empirically in the published reports. Taguchi method is used to study dependency of the rate constant on temperature, reactants’ concentration, and catalyst loading for the synthesis of biodiesel from sulfuric acid-catalyzed esterification of free fatty acid (FFA) with methanol. On the basis of general literature on dependency of rate constant on reactants’ concentration and the esterification-rate determining step, concentration term embedded in the units of SRC has been identified as catalyst concentration. Accordingly SRC has been modified to include the catalyst concentration in the rate law, which is consistent with the general mass-action rate law reported by Blum and Luus (1964) and Pekař (2011). Analysis of the modified rate constant showed it to be independent of the reactants’ concentration. It is thus named as 'concentration independent rate constant (CIRC)'. The predictions of kinetics of the esterification of FFA are better using CIRC than other commonly used rate forms. The modified rate constant is shown to be equivalent to Brønsted–Bjerrum relation. Moreover, the modified rate constant is more general than the reported ones for esterification of fatty acids and it predicts kinetics well over a wide range of reaction parameters.
      Graphical abstract image Highlights (a) Taguchi analysis for parametric effects on concentration-independent rate constant (CIRC or k'). (b) Arrhenius plots for CIRC (using standard L9 orthogonal array design).

      PubDate: 2014-01-15T21:07:17Z
       
  • Multistage centrifugation method for determination of filtration and
           consolidation properties of mineral and biological suspensions using the
           analytical photocentrifuge
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Maksym Loginov , Nikolaï Lebovka , Eugene Vorobiev
      The article describes a new method of multistage centrifugation (MC) for determination of filterability (local filtration and consolidation properties) of mineral and biological suspensions. The method comprises centrifugal compression–permeability and sedimentation–consolidation experiments, performed with the help of analytical photocentrifuge at different centrifugal rotation speeds. The experimental procedure implies determination of the analytical centrifugation curves: dependencies of (i) sediment height on centrifugal acceleration in sedimentation–consolidation experiments and (ii) permeate volume and filter cake dryness on centrifugation time and centrifugal acceleration in filtration–consolidation experiments. The combined analysis of these curves yields the pressure dependencies of local cake dryness, specific cake resistance, and consolidation coefficient in the wide range of solid pressure (5×103–5×105 Pa). Application of MC requires a relatively small quantity of suspension (about 2ml). The method was tested for suspensions with different filterabilities and compressibilities: calcium carbonate, kaolin and yeast suspensions. The pressure dependencies of cake dryness, specific cake resistance, and consolidation coefficient, determined by MC, were in correspondence with those determined in the series of conventional constant pressure dead-end filtration–consolidation experiments.
      Graphical abstract image

      PubDate: 2014-01-15T21:07:17Z
       
  • Experimental investigations on temperature variation and inhomogeneity in
           a packed bed CLC reactor of large particles and low aspect ratio
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Xueyan Guo , Yanli Sun , Rui Li , Fan Yang
      Packed bed reactors with large particles and low aspect ratio are meaningful in engineering for pressure drop reduction and better heat removal. Experimental investigations have been carried out on the transient temperature variation and inhomogeneity in a packed bed reactor with an aspect ratio of 9.5 and filled with particles with an average diameter of 4.53mm for methane–copper/copper oxide chemical looping combustion (CLC). The bed temperature evolution and spatial variation at axial and radial positions were measured and analyzed for oxidation reaction. The development of axial temperature front is found to be much slower than in the fine particle situation in the literature that is typical in laboratory reactors. The axial temperature profile is also apparently diffusion-like, instead of being almost a discontinuously sudden change in fine particle reactors. The phenomena indicate that internal diffusion significantly influences heat transfer in the situation of the large particle size. Wall effects and radial temperature variation in this low aspect ratio reactor were analyzed as well; the reactor experiences strong non-uniform radial temperature distribution, and channeling flow affects significantly the near-wall temperature profile. A 2D unsteady pseudo-homogeneous effective parameter model with radial and axial dispersion was developed to predict the transient heat transfer in the CLC process. A radially variable heat source term was added to the model to represent the effects of the non-uniform distribution of oxygen carrier material in the radial direction. The model predicts qualitatively reasonable 2D temperature distribution, especially the large radial temperature gradient which has been observed in the experiments. The predicted temperature front was a very abrupt change like a discontinuity face which is apparently different from the measured one in the experiments. Without including influences of the wall effects in the model, the used effective thermal conductivities were considered to be underestimated for conditions in the present study.


      PubDate: 2014-01-15T21:07:17Z
       
  • Process parameter optimization through Design of Experiments in synthesis
           of high cis-polybutadiene rubber
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Madhuchhanda Maiti , Vivek K. Srivastava , Satish Shewale , Raksh Vir Jasra , Ankur Chavda , Siddharth Modi
      The neodymium octanoate (Nd), diethylaluminum chloride (DEAC) and triethylaluminum (TEAL)-based catalyst system was studied for polymerization of 1,3-butadiene (BD). The present paper deals with the identification of linear, square and interaction effects of the process parameters on conversion, molecular weight and microstructure of the polybutadiene rubber and consequently the optimization of polymerization process using statistical tool, Design of Experiments. The process comprises of two steps: (1) active catalyst formulation and (2) polymerization of BD. Both steps were optimized sequentially using Box–Behnken design (BBD) and each BBD has three independent variables. In both designs and models, the proposed correlations represent the experimental data adequately for response variables viz. conversion, molecular weight and cis-content. Optimum catalyst formulation was observed to be BD/Nd, DEAC/Nd and TEAL/Nd molar ratio of 902.88, 1.74 and 27.51, respectively. Optimum polymerization conditions were monomer concentration 22%, reaction time 3.3h and reaction temperature 42°C for the said catalyst system.


      PubDate: 2014-01-15T21:07:17Z
       
  • Chemical potential analysis for directing the optimal design of gas
           membrane separation frameworks
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Xuehua Ruan , Gaohong He , Baojun Li , Xiaoming Yan , Yan Dai
      Thermodynamic analysis can discern those energy requirements which might be decreased in the separation system. In this work a theoretical model based on nonequilibrium thermodynamics was established to analyze the free energy change and the key points governing separation efficiency in gas membrane separation. Mass transfer in membranes was treated to be a two-step process in the model: species selectively permeate across membrane to form a series of local permeate gases, then the local permeate gases converge into a bulk permeate stream. Thus the total work required by the membrane process was identified as (i) the work to drive mass permeation, (ii) the work wasted by permeate mixing, and (iii) the minimum separation work. The analysis of two typical systems – the recycle membrane cascade (RMC) and the continuous membrane column (CMC) – revealed that the work wasted by permeate mixing seriously affects the free energy efficiency. This work wastage can be reduced by retrofitting process frameworks. Subsequently, the analysis was used to identify the serious work-losing stages in the RMC. Finally, a partially retrofitted RMC was proposed with tangible reductions in both equipment investment and energy consumption.


      PubDate: 2014-01-15T21:07:17Z
       
  • Molecular simulation of nano-dispersed fluid phases
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Martin Horsch , Hans Hasse
      Fluid phase equilibria involving nano-dispersed phases, where at least one of the coexisting phases is confined to a small volume, are investigated by molecular dynamics simulation. Complementing previous studies on nanoscopic droplets, simulation volumes containing a nanoscopic gas bubble surrounded by a subsaturated liquid phase under tension, i.e. at negative pressure, are conducted in the canonical ensemble. The boundary conditions are chosen such that the phase equilibrium at the curved interface is thermodynamically stable. Two distinct size-dependent effects of opposite sign are found for the density of the gas in the centre of the bubble. The curvature dependence of the surface tension is considered, employing an approach based directly on the average radial density profiles.


      PubDate: 2014-01-15T21:07:17Z
       
  • Three-dimensional simulation of dense suspension upflow regime in
           high-density CFB risers with EMMS-based two-fluid model
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Quan Zhou , Junwu Wang , Jinghai Li
      Dense suspension upflow (DSU) regime in high-density circulating fluidized bed (CFB) risers, featuring no downward particle flux and high mean solid holdup, offers significant advantages over conventional fast fluidization, such as much less solid backmixing and higher solid holdup. While most of the previous CFD simulations are limited to the regime of fast fluidization in low-density CFB risers, it is difficult to reproduce the hydrodynamics of DSU regime using CFD simulation. In this study, a recently proposed EMMS-based two-fluid model (Wang et al., 2012. Chem. Eng. Sci. 75, 349–358), where the particle-rich dense phase and gas-rich dilute phase are treated as the two interpenetrating continua instead of treating gas and solid phases as interpenetrating continua as in standard two-fluid models, is first modified and then used to study the hydrodynamics of high-density CFB risers. Extensive simulations have been performed, and the comparison with experimental data indicated that the EMMS-based two-fluid model had the ability to correctly capture main features of the DSU regime. Therefore, present study not only provided further validation of the idea and feasibility of EMMS-based two-fluid model, but also offered new possibility to explore the hydrodynamic characteristics of DSU regime in high-density CFB risers.


      PubDate: 2014-01-11T20:18:58Z
       
  • Amino acid salts for CO2 capture at flue gas temperatures
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Chiao-Chien Wei , Graeme Puxty , Paul Feron
      The amino acid salt potassium taurate has potential for use as a high-temperature absorbent for post-combustion CO2 capture, because of its low volatility and high absorption rate. In this study, the densities and viscosities of 2–6M taurate solution were determined over the temperature range of 293–353K. We found that the CO2 solubility of taurate solutions, measured using a stirred-cell reactor, is comparable to that of alkanolamines at high temperatures. The absorption rate of CO2 into CO2-free and CO2-loaded taurate solutions was determined using a wetted-wall column. The KG of 4M taurate at 353K is similar in magnitude to the KG of 7m monoethanolamine (MEA) at 313K. We also found that the KG of taurate decreased with increased CO2 loading, although the K G values of taurate solutions are still comparable to CO2-loaded 7m MEA solution. The reaction rate constant of taurate carbamate formation in this work agrees well with published values.


      PubDate: 2014-01-11T20:18:58Z
       
  • Combustion synthesis and characterization of TaC, TaC/TaSi2, and TaC/TaB
           nanoparticles
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Young-Jun Lee , Seung Hyun Kim , Tae-Hyuk Lee , Hayk H. Nersisyan , Kap-Ho Lee , Moon-Hee Han , Seong-Uk Jeong , Kyoung-Soo Kang , Ki-Kwang Bae , Jong-Hyeon Lee
      Herein, we present the low-temperature solid-phase combustion synthesis of tantalum carbide (TaC), TaC/tantalum silicide (TaSi2), and TaC/tantalum boride (TaB) nanoparticles by the silicothermic reduction of potassium fluorotantalate (K2TaF7) in the presence of carbon, boron, and polytetrafluoroethylene (PTFE, 1 1 BJH, Barrett–Joyner–Halenda; HRTEM, high-resolution transmission electron microscopy; MMC, metal matrix composite; PFTE, polyfluorotetraethylene; PTFE; polytetrafluoroethylene; RF, radio frequency; SAED, selected area electron diffraction pattern; T c , combustion temperature; TEM, transmission electron microscopy; U c , combustion velocities; XRD, X-ray diffractometer. (C2F4) n ). The temperature–time profiles of the combustion wave were measured by thermocouples and used to calculate the combustion parameters: temperature and wave velocity. The flame temperature was found to increase with the concentration of PTFE. Using high resolution transmission electron microscopy, a homogeneous distribution of highly crystalline nanoparticles was observed. The thermal–kinetic activation energy, the heat released during each of the individual reactions, and the chemical mechanism of the overall combustion process are discussed with respect to the final products.
      Graphical abstract image

      PubDate: 2014-01-11T20:18:58Z
       
  • Analytical solutions and moment analysis of general rate model for linear
           liquid chromatography
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Shamsul Qamar , Javeria Nawaz Abbasi , Shumaila Javeed , Andreas Seidel-Morgenstern
      The general rate model (GRM) is considered to be a comprehensive and reliable mathematical model for describing the separation and mass transfer processes of solutes in chromatographic columns. However, the numerical solution of model equations is complicated and time consuming. This paper presents analytical solutions of the GRM for linear adsorption isotherms and different sets of boundary conditions at the column inlet and outlet. The analytical solutions are obtained by means of the Laplace transformation. Numerical Laplace inversion is used to transform back the solution in the time domain because analytical inversion cannot be obtained. The first four temporal moments are derived analytically using the Laplace domain solutions. The moments of GRM are utilized to analyze the retention times, band broadenings, front asymmetries and kurtosis of the elution profiles. Relationships are derived among the kinetic parameters to match the first four moments of GRM and the simpler lumped kinetic model (LKM). For validation, the analytical solutions are compared with numerical solutions of a second order finite volume scheme. Good agreements in the results verify the correctness of analytical solutions and the accuracy of the numerical scheme.


      PubDate: 2014-01-11T20:18:58Z
       
  • Table of Contents
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106




      PubDate: 2014-01-11T20:18:58Z
       
  • Influence of the three way catalytic converter substrate cell density on
           the mass transfer and reaction resistances
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Helder Santos , Mário Costa
      The conversion of pollutants in automotive three way catalytic converter (TWC) channels is influenced by fluid mechanics, heat and mass transfer and catalytic reactions. The quantification of the total and relative importance of the physical and chemical phenomena involved is of major importance for the TWC performance optimization. In this paper, we present and implement a method to quantify the magnitudes of the external and internal mass transfer resistances as well as the chemical reaction resistance. The resistance quantification method was applied to analyze the influence of the TWC substrate cell density on the mass transfer and reaction resistances. Two TWCs with different cell density, referred to as TWC 200 cpsi and TWC 400 cpsi, were investigated. The experimental data were obtained under real world TWC operating conditions. For both TWCs and over the range of operating temperatures investigated the results reveal that (i) the magnitude of the reaction resistance is insignificant, (ii) the magnitude of the internal mass transfer resistance is higher than the magnitude of the external mass transfer resistance, and (iii) the washcoat thickness of the TWCs investigated (δ C =30μm) is so high that limits the contact between the reactants and the PCM. A comparison between the two TWCs indicates that (i) the magnitude of the external mass transfer resistance for the TWC 200 cpsi is higher than that for the TWC 400 cpsi, and (ii) the magnitude of both the internal mass transfer and the reaction resistance for the TWC 200 cpsi is lower than those for the TWC 400 cpsi. The present study also demonstrates that, keeping constant both the PCM loading and the washcoat mass, a TWC with high cell density along with a thinner washcoat layer allows reducing simultaneously the external and internal mass transfer limitations, which may enhance further the TWC conversions.


      PubDate: 2014-01-07T19:45:43Z
       
  • Numerical simulation of slag foaming on bath smelting slag
           (CaO–SiO2–Al2O3–FeO) with population balance modeling
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): M.A. Sattar , J. Naser , G. Brooks
      A computational fluid dynamic (CFD) model has been developed for the simulation of slag foaming on bath smelting slag (CaO–SiO2–Al2O3–FeO) by considering foam as a separate phase. The CFD model has been used to predict the foam height, bubble number density and the multiphase flow phenomena in the system. The height of foam is dynamically balanced by the formation of foam due to transformation of both gas and liquid into foam and its destruction due to liquid drainage and bursting of bubbles, transforming foam back to liquid and gas. The bubble break-up and coalescence were considered in gas–liquid dispersion whereas in the foam layer, the bubble coalescence due to film rupture was incorporated. A population balance modeling was used to track the number density of different bubble classes and fixed pivot method was used to discretize the population balance equation. The model predicted the foam height of the slag system (CaO–SiO2–Al2O3–FeO). The content of FeO was changed and its effect on the foam height predicted. The foaming index was calculated and the results from the model predict that the foaming index decreases with increase of FeO content in slag. The CFD model also predicts that the foaming index of a slag with Al2O3 is higher than that of slag without Al2O3. Dimensionless analysis was performed based on the model available in the literature to correlate the foaming index with the physical properties of the slag. The predicted results from the present study are in reasonable agreement with available experimental data.
      Graphical abstract image

      PubDate: 2014-01-03T16:56:30Z
       
  • Mathematical model for solids transport power in a decanter centrifuge
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): George R.A. Bell , Digby D. Symons , John R. Pearse
      A mathematical model of the transport of sedimented solids within a decanter centrifuge has been developed. The primary purpose of the model is to calculate the power, torque and axial force required for the scroll to transport the solids along the bowl. The model is presented in a non-dimensional form and the procedure for implementing the model is included. The model is compared to test data from an existing publication; there was good agreement between the model and data. Example results are presented in the form of graphs to illustrate the influence of key parameters.
      Graphical abstract image

      PubDate: 2014-01-03T16:56:30Z
       
  • Dispersions in crystal nucleation and growth rates: Implications of
           fluctuation in supersaturation
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Meenesh R. Singh , Doraiswami Ramkrishna
      Crystallization is one of the most commonly used and relatively well explored techniques in industries. Yet there are beleaguering issues towards fundamental understanding of this process. One of the curious observations is the appearance of unavoidable dispersions in nucleation and growth rates of crystalline materials grown under homogenous bulk conditions. These dispersions can contribute significantly towards polydispersity in crystalline products. The classical models such as Gibbs critical nucleation theory and Burton–Cabrera–Frank growth models primarily relate nucleation and growth to supersaturation. Therefore, the dispersions in nucleation and growth rates can be related to the local fluctuations in supersaturation. These local fluctuations are driven by the Brownian motion of solute molecules which affects the local concentration and temperature and hence supersaturation. This article presents a stochastic model to describe fluctuations in supersaturation and thereby dispersions in crystalline materials. The stochastic model is derived from the framework of density and temperature fluctuations. The resulting dispersions in size and shape of nuclei are obtained by multi-dimensional maximization of Gibbs free energy in morphology domain of potassium acid phthalate. The model predictions are validated with the experimental measurements of growth rate dispersions in potassium acid phthalate crystals. The proposed framework provides the first ab initio predictions for the observed dispersions in crystallization processes.
      Graphical abstract image

      PubDate: 2014-01-03T16:56:30Z
       
  • Liquid entrainment behavior at the nozzle exit in coaxial gas–liquid
           jets
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Xiu-Shan Tian , Hui Zhao , Hai-Feng Liu , Wei-Feng Li , Jian-Liang Xu
      The near-field flow behavior of coaxial gas–liquid jets has a significant influence on the atomization performance and life cycle of atomizers, and the present study focused on this issue. The flow visualization technique was employed to examine liquid entrainment behavior near the nozzle. The thick central tube affected both gas and liquid flow fields. Liquid entrainment could be observed in the near-field with the increase in gas velocity, and a liquid “bulge” structure was induced on the surface of the near-field liquid jet for the first time. The formation mechanism and dynamic characteristics of the “bulge” were studied. Two critical situations in the liquid entrainment process to the surface of the central tube were identified as “initial entrainment” and “full entrainment”. The two critical situations were studied in a convective gas–liquid layer in the recirculation region based on total pressure conservation theory. The theoretical models for the two situations were obtained, and these models agreed well with the experimental results.


      PubDate: 2014-01-03T16:56:30Z
       
  • Nanopillar array with multi-scale inter-pillar spacing as chromatography
           stationary phase support: Theoretical performance evaluation
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Xiaohong Yan , Nan Li
      Nanopillar arrays with nanoscale inter-pillar spacing can be fabricated with increasingly high precision in recent years. We propose to use nanopillar arrays with multi-scale inter-pillar spacing to play the role of porous microstructures in columns for pressure driven liquid chromatography. The pattern of the nanopillar array is adjusted to create special “core–shell” or “totally porous” structures with multi-scale ordered pores. We predict the column performance and the pressure drop of the hypothetical columns by a theoretical model with the aid of the pore scale numerical simulation. The prediction indicates that hypothetical columns have better column performance than that of a real column filled with vertically aligned “core–shell” micropillars with ordered inter-pillar pores but disordered intra-pillar pores. We attribute the better performance of hypothetical columns to the multi-scale ordered, size controllable pores in the special “core–shell” or “totally porous” structures. We also investigate the effect of the velocity slip that may occur at hydrophobic nanopillar surfaces and show that further column performance improvement and flow rate enhancement can be expected.
      Graphical abstract image

      PubDate: 2014-01-03T16:56:30Z
       
  • Influence of spinning cup and disk atomizer configurations on droplet size
           and velocity characteristics
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Mahmoud Ahmed , M.S. Youssef
      The influence of spinning cup and disk atomizer configurations on droplet size and ejection velocity characteristics has been experimentally investigated. The Phase Doppler Particle Analyzer (PDPA) was used to measure spray characteristics in the downstream tangential distance along the spray trajectory. Four groups of both rotating disks and cups with different configurations have been experimentally studied. The first group comprises spinning disks serrated with different numbers of teeth ranging from 0 to 240. The second group includes spinning disks with different upper and lower edge angles in the range of 15° to 60°. The third set consists of spinning conical cups with different half cone angles ranging from 15° to 60° and different base diameters in the range of 0.002 to 0.06m (2–60mm). The last set includes spinning cylindrical cups with different heights in the range of 0.005to 0.045m (5–45mm). The outer diameter of all cups and disks in all sets is 0.07m. All experimental tests have been performed at a rotating speed of 1257rad/s (12,000rpm), and supply water flow rate of 2.22×10−6 m3/s (8L/h). Measurements of Sauter mean diameter and average droplet velocity for droplets produced by studied cups and disks are compared with those of droplets produced by a regular flat disk atomizer. Comparisons indicate that all values of Sauter mean diameters and average droplet velocities for different configurations are statistically within 95% confidence level intervals around the mean of those produced by a regular flat disk. Numerically, the mean of Sauter mean diameters produced by different configurations of spinning disk and cup atomizers varied between −8% and 12% around the mean of Sauter mean diameter produced by a regular flat disk. In addition, the virtual slip ratio ranged between 18% and 41% for all atomizer configurations, while for a regular flat disk, it was 33%. The developed correlation predicting Sauter mean diameter produced by spinning regular flat disks can be satisfactorily used to predict those produced by rotating cup and disk atomizers with different configurations. In addition, the values of drag coefficient and drag force for droplets of a regular flat disk are slightly different from those calculated for investigated disk and cup atomizers.


      PubDate: 2014-01-03T16:56:30Z
       
  • Liquid film thickness behaviour within a large diameter vertical 180°
           return bend
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): M. Abdulkadir , A. Azzi , D. Zhao , I.S. Lowndes , B.J. Azzopardi
      Experimental results of liquid film thickness distribution of an air–water mixture flowing through a vertical 180° return bend are reported. Measurements of liquid film thickness were achieved using flush mounted pin and parallel wire probes. The bend has a diameter of 127mm and a curvature ratio (R/D) of 3. The superficial velocities of air ranged from 3.5 to 16.1m/s and those for water from 0.02 to 0.2m/s. At these superficial velocity ranges, the flow pattern investigated in this work focused on churn and annular flows. It was found that at liquid and gas superficial velocities of 0.02m/s and 6.2m/s, respectively, the averaged liquid film thickness peak at 90°. At gas superficial velocity of 16.1m/s, the relationship between them is linear due to the shear forces overcoming gravity. Additionally, it was found that deposition of entrained droplets keeps the liquid film on the outside of the bend. The results of polar plots of average liquid film thickness in the bend showed that the distribution of the liquid film is not symmetrical with thicker films on the inside of the bend due to the action of gravity. Experimental results on average liquid film thickness showed good agreement with the simulation data reported in the literature.


      PubDate: 2014-01-03T16:56:30Z
       
  • Boundary conditions and phase functions in a Photo-CREC Water-II reactor
           radiation field
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): P.J. Valades-Pelayo , J. Moreira , B. Serrano , H. de Lasa
      This study analyses issues and limitations regarding the definition of the local volumetric rate of photon absorption (LVRPA) in an annular Photo-CREC Water II reactor. This analysis is carried out in order to establish the influence of the scattering phase functions and boundary conditions (BC) on the LVRPA. To accomplish this, macroscopic radiation quantities such as the total rate of photon absorption (TRPA) and the total transmitted radiation (TT) as functions of photocatalyst concentration are experimentally determined. On the other hand, the radiative transfer equation (RTE) is solved using a Monte Carlo method (MC). Boundary conditions accounting for lamp absorption/re-emission effects and diffuse reflection/absorption at the inner and outer reactor walls are employed. The Henyey–Greenstein and the binomial phase functions are used to simulate both forward and backward scattering phase functions. The significant influence of the phase functions on the radiation field is assessed for various BCs. Simulation results show that in annular photo-reactors, the sensitivity of the LVRPA towards the “g” scattering parameter increases when “g” is set in the forward scattering range. Moreover, the comparison with experimental macroscopic quantities proves that Degussa P25 displays mostly forward scattering. The investigation of various possible BCs also proves that TT and TRPA fitting yields scattering parameters in restricted ranges. Consideration of the more physically sound BCs applicable in the Photo-CREC Water II, with complete absorption in the outer wall leads to a “g” value in the 0.6–0.8 range. It is proven that the MC simulation and the use of TT measurements in the Photo-CREC-Water II reactor with selected BCs are of critical importance for establishing phase functions and scattering parameters in photo-catalytic reactors.
      Graphical abstract image

      PubDate: 2014-01-03T16:56:30Z
       
  • A mechanistic population balance model for granulation processes: Effect
           of process and formulation parameters
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Anwesha Chaudhury , Huiquan Wu , Mansoor Khan , Rohit Ramachandran
      This work is concerned with the theoretical development of a semi-mechanistic aggregation kernel in a population balance model (PBM) which takes into account the effect of droplet spreading on a particle surface that aids in the coalescence of particles. Empirical aggregation kernels are more commonly used in simulations however they do not reflect the true physics of the system. The proposed kernel is computationally less expensive, yet it takes into account the various key operating parameters that affect the process. The kernel has been validated qualitatively and the lumped and distributed properties show good agreement with the expected behavior of the process. The various empirical parameters present in the granulation model have been identified and expressed as a function of the measurable operating quantities, thus providing a better knowledge regarding the effect of the process parameters on the final product with the help of a more fundamental, first principle based model. A detailed sensitivity analysis (involving viscosity, impeller speed, contact angle and liquid spray rate) has also been conducted in order to study the influence of the process parameters on the final granule properties. This knowledge provides a theoretical basis for the high-shear wet granulation process design space development. The model has also been able to successfully capture the steady and induction behavior of the process under the expected operating conditions.


      PubDate: 2013-12-30T16:15:46Z
       
  • Simulation and eigenmode analysis of advective–diffusive transport
           in micromixers by the diffusive mapping method
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): O. Gorodetskyi , M.F.M. Speetjens , P.D. Anderson
      Advective–diffusive transport in microflows is studied by means of the diffusive mapping method, a recent extension of the mapping method by Gorodetskyi et al. (2012. Phys. Fluids 24) that includes molecular diffusion. This greatly expands the application area of the mapping technique and makes the powerful concepts of eigenmode decomposition and spectral analysis of scalar transport accessible to an important class of flows: inline micromixers with diffusion. The staggered herringbone micro-mixer is adopted as a prototypical three-dimensional micro mixer. Simulations with the diffusive mapping method are in close agreement with experimental observations in the literature and expose a strong impact of diffusion on the transport. Diffusion enables crossing of Lagrangian transport barriers and thus smoothens concentration gradients and accelerates homogenization. Spectral analysis of the mapping matrix reveals that this already occurs on a modal level in which individual eigenmodes progressively smoothen and spread out across transport barriers with stronger diffusion. Concurrently, the corresponding eigenvalues diminish and thus fundamentally alter the mixing process by invariably causing homogenization, irrespective of the Lagrangian flow structure. This happens faster and exhibits an earlier emergence of the dominant eigenmode the stronger the diffusion. Lagrangian structures may still affect the spectral properties in that flows comprising both islands and chaotic seas typically result in a richer set of eigenmodes compared to cases with global chaos.
      Graphical abstract image Highlights

      PubDate: 2013-12-30T16:15:46Z
       
  • Quantification of trace element emissions from low-carbon emission energy
           sources: (I) Ca-looping cycle for post-combustion CO2 capture and (II)
           fixed bed, air blown down-draft gasifier
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): A. Cotton , K.N. Finney , K. Patchigolla , R.E.A. Eatwell-Hall , J.E. Oakey , J. Swithenbank , V. Sharifi
      The integrated technologies of gasification and the calcium looping cycle represent the opportunity to produce H2 as an energy carrier while ensuring inherent CO2 capture, thus producing a near-zero or negative emission fuel. Gasification of waste-derived fuel including demolition wood and low density plastic is gaining in interest due to the potential to minimise waste to landfill, whilst also representing a carbon-neutral energy source. However, potential trace element emissions from the gasification of such fuels require investigation to ensure compliance with targets under the EU Ambient Air Quality Directive 2008 and the UK Air Quality Standards Regulations 2010. Likewise, contaminants present in limestone have the potential to be released to the environment under the operating regimes required for carbonation and calcination in the calcium looping cycle for CO2 capture. Solid samples (offline), liquids (offline) and gaseous (offline/online and in-situ mobile ICP-OES) products from a pilot scale fixed bed, air-blown down-draft gasifier and from a pilot scale CO2 capture reactor comprising of the calcium looping cycle, have been collected and analysed in order to gain further understanding of the likely trace element partitioning in both processes. Results showed that a number of trace element contaminants present in the original CO2 sorbent and gasifier fuel samples were also present in the flue gas from both the CO2 capture and gasification processes, implying that integration of the technologies may result in enhanced contamination in the final gaseous product. The main outputs of this study assist in analysing plant requirements, for example gas cleaning, and identifying the environmental emissions and residual disposal.


      PubDate: 2013-12-30T16:15:46Z
       
  • Modeling and control of crystal shape in continuous protein
           crystallization
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Joseph Sang-Il Kwon , Michael Nayhouse , Panagiotis D. Christofides , Gerassimos Orkoulas
      In this work, a continuous crystallization process with a fines trap is modeled in an effort to produce tetragonal hen-egg-white (HEW) lysozyme crystals with a desired shape distribution. The crystal shape of tetragonal lysozyme crystals is defined by the aspect ratio of the crystal heights in the direction of the (110) and (101) faces. A kinetic Monte Carlo (kMC) simulation is used to model the crystal nucleation, growth, and dissolution through a fines trap in a continuous crystallization process. Specifically, the crystal growth processes are simulated through adsorption, desorption, and migration mechanisms, and the crystal growth rates are calibrated through experimental data (Durbin and Feher, 1986). Additionally, a nucleation rate expression is developed based on the results from an experimental work (Galkin and Vekilov, 2001) to simulate the crystals nucleated at different times. Then, the method of moments is used to approximate the dominant behavior of a population balance equation (PBE) describing the evolution of the crystal volume distribution through the three leading moments. The moment model is used, along with solute mass and energy balance equations, to design a model predictive controller (MPC), which allows for the crystallizer to produce crystals with a desired shape distribution. In the proposed MPC, the jacket temperature is manipulated to appropriately suppress the influence of undesired effects such as process disturbances and measurement noise, while handling significant changes in the set-point value. Furthermore, it is demonstrated that a continuous process with a fines trap can produce crystals with a low polydispersity.


      PubDate: 2013-12-30T16:15:46Z
       
  • Prerequisites for achieving gold adsorption by multiwalled carbon
           nanotubes in gold recovery
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Siu-Kwong Pang , Kam-Chuen Yung
      The use of multiwalled carbon nanotubes (MWCNTs) in gold recovery is proposed, wherein MWCNTs are employed to adsorb gold from the acidic AuCl4 − solutions produced in the lixiviation process in the semiconductor and waste electrical and electronic equipment treatment industry. In the present study, HAuCl4 in hydrochloric acid solutions were prepared to mimic the gold solutions produced in the lixiviation process, and batch shaking adsorption experiments were performed to examine the adsorption characteristics of AuCl4 −. After 24h of adsorption, nearly 100% gold adsorption could be achieved at a 5g/L dose of MWCNTs when the initial gold concentration was 200mg/L. The gold adsorption approached a plateau level after 20min. Moreover, MWCNTs have a larger adsorption capacity and a higher adsorption rate when compared with ion exchange resins and activated carbon because MWCNTs have a greater surface area. After adsorption, elemental gold on the MWCNTs was discovered by means of transmission electron microcopy (TEM), electron diffraction and electron dispersive X-ray spectrometry (EDS). From X-ray photoelectron spectrometry (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), AuCl2 − and Au on the MWCNTs were detected. Therefore, it is suggested that AuCl4 − is reduced to Au directly and/or through an intermediate AuCl2 − by MWCNTs, and subsequently, Au is deposited on the MWCNTs. The Au adsorption on MWCNTs follows pseudo-second-order kinetics and the Langmuir isotherm. Au adsorption on MWCNTs is not highly affected by Cu2+ even for solutions containing high concentrations of Cu2+. While the Cu concentration was 10000mg/L, the percentage of Au adsorption was around 97%, however, only around 1% of Cu was adsorbed. The reasons why MWCNTs exhibit much greater Au adsorption than Cu adsorption are that the standard reduction potential for AuCl4 −/Au is more positive than that for Cu2+/Cu, and the standard reduction potential for MWCNTs is in-between them.


      PubDate: 2013-12-30T16:15:46Z
       
  • Mixed matrix membranes comprising MOFs and porous silicate fillers
           prepared via spin coating for gas separation
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Philipp Burmann , Beatriz Zornoza , Carlos Téllez , Joaquín Coronas
      Different types of fillers of inorganic (titanosilicate ETS-10 and mesoporous silica type MCM-41) and organic-inorganic nature (ZIF-8 and NH2-MIL-53), with different pore size (micro- and mesoporosity) and structure, diverse particle shape, and particle sizes in the 85–400nm range were embedded in a polysulfone matrix via spin coating. Spin coating technology, widely used in the production of thin and uniform layers on porous substrates was used here to fabricate in one coating step symmetric mixed matrix membranes (MMMs) by adjusting the spinning disk velocity, rotational time, and solid concentration and volume of solution. By selecting the optimal parameters, homogeneous MMMs containing 8wt% of the various fillers were obtained and tested for H2/CH4 and O2/N2 mixed-gas separations, achieving significant improvements over the neat polymer. While NH2-MIL-53 MMMs revealed the highest separation performance (a rise in selectivity higher than 60 % compared to the pure polymer for H2/CH4 and O2/N2 separations), ZIF-8 MMMs showed a substantial increase in permeability (from 12.7 to 51.4 Barrer for H2, and from 2.0 to 6.1 Barrer for O2). Besides, the spin coating process enhanced solvent evaporation and reduced coat production time compared to the traditional by-hand casting.
      Graphical abstract image

      PubDate: 2013-12-30T16:15:46Z
       
  • Quantitative kinetic inhibitor comparisons and memory effect measurements
           from hydrate formation probability distributions
    • Abstract: Publication date: 7 April 2014
      Source:Chemical Engineering Science, Volume 107
      Author(s): Eric F. May , Reuben Wu , Malcolm A. Kelland , Zachary M. Aman , Karen A. Kozielski , Patrick G. Hartley , Nobuo Maeda
      In contrast with conventional experiments for ranking the performance of kinetic hydrate inhibitors (KHIs), the high pressure automated lag time apparatus (HP-ALTA) is not limited by the stochasticity of hydrate formation because it can make large numbers of formation measurements rapidly. An improved procedure for analysing HP-ALTA data is presented here in which formation probability density histograms with uniform temperature bin widths are constructed. Operations such as numerical integration and subtraction can then be applied to entire formation distributions without the need to regress the data to model analytic functions. This approach enables apparatus effects on the measured formation distributions to be quantified and mitigated. Using analogue natural gas mixtures, a demonstration of the improved method is reported here for six KHIs that were also tested using a conventional rocking cell. The cumulative formation probability distribution functions determined by numerical integration of the histograms were used to quantitatively (1) assess the performance of the KHIs, (2) study the memory effect in pure water, and (3) assess its impact on the performance of each KHI. The rankings of the KHIs obtained from the various performance metrics accessible through the HP-ALTA data were generally consistent with the rocking cell rankings, with the average absolute deviation in net subcooling for the two apparatus being 2 to 3K. In the quiescent HP-ALTA samples, the three worst performing KHIs still had expected subcoolings of about 14K unless the memory effect was present, in which case the expected net subcoolings of the three worst performing KHIs ranged from 0–6K. In contrast the memory effect reduced the expected subcoolings of the three best performing KHIs by only 1–2K. Using the new method of analysis, hydrate formation distributions measured with the HP-ALTA can also be used to identify regions of good and poor performance for a given KHI, which might aid in the determination of improved inhibition strategies or assist the development of improved hydrate inhibitors.


      PubDate: 2013-12-26T15:57:29Z
       
  • Efficient biosynthesis of glycyrrhetic acid 3-O-mono-β-d-glucuronide
           (GAMG) in water-miscible ionic liquid by immobilized whole cells of
           Penicillium purpurogenum Li-3 in alginate gel
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Imdad Kaleem , Huang Shen , Bo Lv , Bin Wei , Aamir Rasool , Chun Li
      Five immobilizing materials were investigated for the catalytic efficiency of whole cells of Penicillium purpurogenum Li-3 (w-PGUS) and alginate gel was found the best polymer for the biotransformation of glycyrrhizin (GL) into glycyrrhetic acid 3-O-mono-β-d-glucuronide (GAMG). The activity of compositionally optimized w-PGUS alginate beads was examined in different ionic liquids (ILs). The 30% (v/v) hydrophilic IL [BMIM]BF4 in reaction mixture exhibited an explicit biocompatibility with alginate support; consequently aggrandized the catalytic efficiency of the immobilized w-PGUS compared with pure buffer and ILs media. The optimal biotransformation conditions of the immobilized w-PGUS were evaluated and compared with buffer and IL co-solvent media: including w-PGUS beads concentration (70g/l vs. 80g/l), substrate concentration (5mM vs. 4mM), temperature (45°C vs. 45°C), pH (5.4 vs. 5.6), and shaking speed (180rpm vs. 160rpm). Under the optimized conditions; the yield of GAMG was 2.62g/l after 62h in IL co-solvent medium compared to 2.34g/l after 72h in buffer medium. The immobilized w-PGUS also retained 45.80% and 18.13% of their original activity in IL co-solvent and buffer media respectively; after ten repeated batches displaying high operational stability for GL biotransformation.


      PubDate: 2013-12-18T14:48:08Z
       
  • Direct discretizations of bi-variate population balance systems with
           finite difference schemes of different order
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Volker John , Carina Suciu
      The accurate and efficient simulation of bi-variate population balance systems is nowadays a great challenge since the domain spanned by the external and internal coordinates is five-dimensional. This report considers direct discretizations of this equation in tensor-product domains. In this situation, finite difference methods can be applied. The studied model includes the transport of dissolved potassium dihydrogen phosphate (KDP) and of energy (temperature) in a laminar flow field as well as the nucleation and growth of KDP particles. Two discretizations of the coupled model will be considered which differ only in the discretization of the population balance equation: a first order monotone upwind scheme and a third order essentially non-oscillatory (ENO) scheme. The Dirac term on the right-hand side of this equation is discretized with a finite volume method. The numerical results show that much different results are obtained even in the class of direct discretizations.


      PubDate: 2013-12-14T14:13:12Z
       
  • Deactivation models by fitting the progression of temperature profiles
           – Coking model for the MTG process in adiabatic reactors
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Martin Dan Palis Sørensen
      A methodology for estimating deactivation models for catalysts in industrial application is proposed. The method applies the movement of the measured axial temperature profile to gain information of the deactivating phenomena. For adiabatic reactors the conditions must be obtained by controlled heat compensation in a reactor furnace. As an example a deactivation model for the industrial methanol-to-gasoline (MTG) process is developed. The deactivation model together with suitable reactor models is a system of coupled partial differential equations with time and spatial coordinate as the independent variables. The unknown model parameters are estimated via a non-linear least square method, by matching predicted axial temperature profiles with measured profiles obtained in a pilot reactor containing a gasoline synthesis test catalyst.


      PubDate: 2013-12-14T14:13:12Z
       
  • Prediction of mass transfer coefficients in a slurry bubble column based
           on the geometrical characteristics of bubbles
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Stoyan Nedeltchev , Krishna D.P. Nigam , Adrian Schumpe
      The experimental volumetric liquid-phase mass transfer coefficients k L a measured in a slurry bubble column (0.095m in ID) operated with several three-phase systems (air–ligroin–polyvinylchloride (PVC), air–ligroin–polyethylene (PE) and air–water–activated carbon) were predicted successfully based on a correction of Higbie's (1935) penetration theory. A correction factor (which is a single function of the Eötvös number) developed earlier (Nedeltchev et al., 2007) in gas–liquid bubble columns was found applicable to slurry bubble columns. It varied from 0.22 to 1.91 in the above-mentioned three-phase systems. As the bubble size becomes bigger, the correction factor increases and vice versa. The two major changes in the algorithm (applied to slurry bubble columns) are associated with the calculation of the Sauter-mean bubble diameter (Lemoine et al., 2008) and the gas–liquid interfacial area. In the case of a slurry bubble column, both the slurry density and effective viscosity were used in the model correlations. It was found that the model yielded good results not only in the homogeneous regime but also in the heterogeneous regime (up to gas velocities of 0.08m/s). It worked also well at relatively high solids concentrations (up to 15%). When the bubble Reynolds number is higher than 700 and when the superficial gas velocity is beyond 0.04m/s, then the penetration theory based on the new definition of the contact time can be applied straightforwardly (without any correction factor). The developed model is applicable to ellipsoidal bubbles and it demonstrates the important effect of the geometrical characteristics (length and height) of these bubbles on the mass transfer coefficients.


      PubDate: 2013-12-14T14:13:12Z
       
  • Robust optimization of periodically operated nonlinear uncertain processes
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Darya Kastsian , Martin Mönnigmann
      We present a method for determining optimal modes of operation for autonomously oscillating systems with uncertain parameters. In a typical application of the method, a nonlinear dynamical system is optimized with respect to an economic objective function with nonlinear programming methods, and stability is guaranteed for all points in a robustness region around the optimal point. The stability constraints are implemented by imposing a lower bound on the distance between the optimal point and all stability boundaries in its vicinity, where stability boundaries are described with notions from bifurcation theory. We derive the required constraints for a general class of periodically operated processes and show how these bounds can be integrated into standard nonlinear programming methods. We present results of the optimization of two chemical reaction systems for illustration.


      PubDate: 2013-12-14T14:13:12Z
       
  • Flow characteristics and rheological properties of natural gas hydrate
           slurry in the presence of anti-agglomerant in a flow loop apparatus
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Ke-Le Yan , Chang-Yu Sun , Jun Chen , Li-Tao Chen , De-Ji Shen , Bei Liu , Meng-Lei Jia , Meng Niu , Yi-Ning Lv , Nan Li , Zhi-Yu Song , Shu-Shan Niu , Guang-Jin Chen
      The flow characteristics and rheological properties of natural gas hydrate slurry, with initial water cuts ranging from 5 to 30vol%, were investigated in a flow loop. The experimental results indicate that the hydrate slurry can be considered a pseudoplastic fluid and presents more obvious shear-thinning behaviour with the increase in the hydrate volume fraction. The study on the fluid morphology demonstrated that the original structure of the water-in-oil emulsion is destroyed by the formation of gas hydrate, and the hydrate slurry is ultimately transported as a solid dispersion system. An empirical Herschel–Bulkley-type equation that considers the hydrate volume fraction was developed to improve the description of the rheological properties of the hydrate slurry. The apparent viscosities of the hydrate slurry calculated by the new equation were in accordance with the experimental data. Shutting-down/restarting tests using three shutting-down times (2h, 4h, and 8h) were performed. The experimental results indicate that the hydrate slurry can be easily and safely restarted from the static state after a long shutting-down period and exhibits obvious thixotropic behaviour with increasing shutting-down time.


      PubDate: 2013-12-14T14:13:12Z
       
  • The potential impact of membrane cascading on downstream processing of
           oligosaccharides
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Nirmal V. Patil , Anja E.M. Janssen , Remko M. Boom
      To assess the potential use of ideal nanofiltration cascades for the industrial fractionation of oligosaccharides, simulations of single, three and five stage NF cascades were carried out. Three and five stage ideal cascades show significant improvement in separation with diafiltration compared to single stage systems. The calculations do imply different membrane areas in each stage of the cascade. The ratio of the sieving coefficients of a binary mixture over the membrane plays an important role in determining the relation between yield and purity in a cascade system. At high sieving coefficient ratios, both yield and purity increase concurrently in a three stage system, whereas at a low ratio of the sieving coefficients, the yield and purity become inversely proportional on the retentate side. In a five stage systems, both yield and purity become inversely proportional at high and low sieving coefficient ratios. A five stage cascade system installation would be optimal for most applications since at very low local separation factors sufficient separation and yield could be achieved.
      Graphical abstract image

      PubDate: 2013-12-14T14:13:12Z
       
  • Rapid and high capacity methane storage in clathrate hydrates using
           surfactant dry solution
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Shuanshi Fan , Liang Yang , Yanhong Wang , Xuemei Lang , Yonggang Wen , Xia Lou
      Surfactant dry solution (DS) was prepared by mixing sodium dodecyl sulfate (SDS) solution, hydrophobic silica nanoparticles and air in a high speed blender. Flour-like SDS-DS combines the advantages of dispersed dry water and active SDS solution. Methane storage in clathrate hydrates using SDS-DS was investigated in a stainless steel vessel without stirring under the condition of 5.0MPa and 273.2K. The results demonstrated that highly dispersed SDS-DS could significantly enhance formation kinetics and storage capacity of methane hydrate. SDS-DS exhibited about the same methane storage capacity (172.96m3 m−3) as dry water, but faster storage rates than dry water. Compared to SDS solution, SDS-DS had similar storage rates (7.44m3 m−3 min−1) and higher methane storage capacity under the relative low pressure. However, the aggregation of partial SDS-DS powders destroyed its original dispersive property after hydrate dissociation.


      PubDate: 2013-12-14T14:13:12Z
       
  • CFD-based compartment model for description of mixing in bioreactors
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Angélique Delafosse , Marie-Laure Collignon , Sébastien Calvo , Frank Delvigne , Michel Crine , Philippe Thonart , Dominique Toye
      In most bioprocesses, it is fundamental to accurately predict the hydrodynamics behavior of bioreactors of different size and its interaction with the biological reaction. Computational Fluid Dynamics can provide detailed modeling about hydrodynamics and mixing. However, it is computationally intensive, especially when reactions are taken into account. Another way to predict hydrodynamics is the use of “Compartment” or “Network-of-zones” model which are much less demanding in computation time than CFD. However, compartments and fluxes between them are often defined by considering global quantities not representative of the flow complexity. To overcome the limitations of these two methods, a solution is to combine compartment modeling and CFD simulations. The aim of this study is to propose a compartment model where the flow rates between two adjacent compartments are easily computed from the velocity fields obtained by CFD. The mixing evolution predicted by the CFD-based compartment model have been then compared with mixing experiment results. Unlike a CFD mixing simulation and a classical compartment model, the CFD-based compartment model proposed in this work reproduces with a good accuracy the spatial distribution of concentrations during the mixing process and this, without any adjustable parameters.


      PubDate: 2013-12-14T14:13:12Z
       
  • Interphase mass transfer coefficient in fluidized bed combustion by
           Eulerian CFD modeling
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Ari Vepsäläinen , Srujal Shah , Jouni Ritvanen , Timo Hyppänen
      Eulerian gas–solid CFD simulations are applied to derive interphase mass transfer coefficients for the Geldart B and D solids in a bench and a pilot size fluidized bed combustion reactor. The interphase mass transfer coefficients obtained from the bubbling and turbulent churning fluidized bed CFD simulations are compared to the empirical data and correlations, which are primarily available only for the Geldart A solids. Particularly, the effect of fluidization velocity, particle diameter and bubble size on the interphase mass transfer coefficients is evaluated.


      PubDate: 2013-12-14T14:13:12Z
       
  • Experimental study of the hydrodynamic behaviour of slug flow in a
           vertical riser
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): M. Abdulkadir , V. Hernandez-Perez , I.S. Lowndes , B.J. Azzopardi , S. Dzomeku
      This paper presents an investigation of the hydrodynamics of slug flow in a vertical 67mm internal diameter riser. The slug flow regime was generated using a multiphase air–silicone oil mixture over a range of gas (0.42<U SG <1.35m/s) and liquid (0.05<U SL <0.38m/s) superficial velocities. Electrical capacitance tomography (ECT) was used to determine: the velocities of the Taylor bubbles and liquid slugs, the slug frequencies, the lengths of Taylor bubbles and the liquid slugs, the void fractions within the Taylor bubbles and liquid slugs and the liquid film thicknesses. A differential pressure transducer was used to measure the pressure drops along the length of the riser. It was found that the translational velocity of a Taylor bubble (the structure velocity) was strongly dependent on the mixture superficial velocity. As the gas superficial velocity, was increased, the void fraction and the lengths of the liquid slugs and the Taylor bubbles were observed to increase. The increase in gas superficial velocity causes an increase in the frictional pressure drop within the pipe, whilst the total pressure drop (which is a sum of the hydrostatic and frictional pressure drop) along the length of the riser decreases. In addition, the frequencies of the liquid slugs were observed to increase as the liquid superficial velocity increases, but to be weakly dependant on the gas superficial velocity. The manual counting method for the determination of slug frequency was found to be in good agreement with the power spectral density (PSD) computed method.


      PubDate: 2013-12-14T14:13:12Z
       
  • Principal component analysis for kinetic scheme proposal in the thermal
           and catalytic pyrolysis of waste tyres
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Roberto Aguado , Aritz Arrizabalaga , Miriam Arabiourrutia , Gartzen Lopez , Javier Bilbao , Martin Olazar
      Principal component analysis is used as a pattern recognition method to find criteria for grouping into lumps the compounds formed in the thermal and catalytic pyrolysis of waste tyres. This information is the stating point for the proposal of simple kinetic schemes that efficiently describe the complex reactions that occur in the pyrolysis process. It has been proven that the kinetic scheme must consider a depolymerization step of the waste to give isoprene and styrene monomers and the dimer of the former (limonene), the formation of primary products (char, tar and gas) by thermal cracking of the original high molecular weight compounds, and the subsequent secondary reactions by thermal cracking of heavy primary fractions (tar) to form lighter fractions (gas, gasoline and C10− aromatics). The use of a catalyst prepared based on a HY zeolite selectively enhances the reactions of condensation and alkylation of limonene and gasoline to aromatics, whereas the one based on a HZSM-5 zeolite selectively enhances the cracking of tar to lighter fractions (gas and C10− aromatics), limonene cracking to isoprene and C5–C10 hydrocarbons or even the cracking of the latter to C1–C4 gases.


      PubDate: 2013-12-10T13:47:46Z
       
  • Design tool and guidelines for outdoor photobioreactors
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Euntaek Lee , Jérémy Pruvost , Xing He , Ramakanth Munipalli , Laurent Pilon
      This study provides design and operational guidelines for achieving maximum biomass productivity in outdoor photobioreactors (PBRs). Detailed simulations of coupled light transfer and growth kinetics of microalgae were performed for open ponds, vertical flat-plate, and tubular PBRs operated in batch mode and exposed to time-dependent collimated and diffuse solar irradiance. The temporal evolution of microalgae concentration was predicted by accounting for light saturation, photoinhibition, and respiration. Three-dimensional spectral light transfer simulations of collimated and diffuse solar radiation in the PBRs were performed at different times of the day. The green microalgae Chlamydomonas reinhardtii was used for illustration purposes. The study demonstrated that the daily productivity per unit of illuminated surface area for PBRs operated in batch mode was identical and depended uniquely on the ratio X 0 / a where X 0 is the initial microalgae concentration and a is the illuminated surface area per unit volume of PBR. A maximum daily productivity of about 0.045kg/m2/day was achieved for X 0 / a = 0.035 kg / m 2 . Remarkably, similar results were obtained with experimental data and other simulation results based on different models reported in the literature, for different microorganisms and PBRs operated in continuous mode. The PBR optical thickness, represented by X 0 / a , constitutes a convenient parameter for designing (via a) and operating (via X 0) these PBRs to achieve their maximum performance.


      PubDate: 2013-12-10T13:47:46Z
       
  • Kinetic modeling of urea decomposition based on systematic
           thermogravimetric analyses of urea and its most important by-products
    • Abstract: Publication date: 17 March 2014
      Source:Chemical Engineering Science, Volume 106
      Author(s): Wolfgang Brack , Barbara Heine , Felix Birkhold , Matthias Kruse , Günter Schoch , Steffen Tischer , Olaf Deutschmann
      A kinetic reaction model for thermal decomposition of urea is presented. Systematic thermogravimetric analyses of urea and its most important by-products, such as biuret and cyanuric acid, are performed to gain the main reactions and their rates. Gaseous products are analyzed and the concentrations of solid products are determined. The reaction scheme, as well as the kinetic parameterization, is validated at different heating rates. The proposed kinetic reaction model matches all performed thermogravimetric analyses and it is also able to reproduce changes in the measurement conditions, such as differences in crucibles geometry or variations of the initial sample mass.


      PubDate: 2013-12-10T13:47:46Z
       
 
 
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